1. Field of the Invention
The present invention relates to a solid carrier for supporting microorganism growth. More specifically, the present invention relates to: a solid, lightweight composite polymeric medium for supporting microorganism growth; a solid carrier useful in catalyzing chemical reactions and/or neutralizing acidic wastes; a solid, lightweight composite polymeric carrier useful in catalyzing chemical reactions and/or neutralizing acidic wastes.
2. Description of the Related Art
Solid carriers for supporting microorganism growth, also known as growth media, are used in a wide variety of industries such as wastewater treatment, production of organic compounds in bioreactors, gas separation, biofilters, remediation of hazardous waste, water treatment and production of fermented products. Some carriers provide an outer surface for attachment and growth of microorganisms while others allow growth on both the surface and on the inside of the carrier. Depending upon the intended purpose, the microorganisms, such as bacteria, algae and/or fungi, are used to either metabolize pollutants, synthesize specific organic compounds from chemical reactants, or ferment sugars into alcohols.
In wastewater treatment, raw sewage is processed into a stream of effluent safe enough to discharge into a body of water. After the raw sewage is subjected to a primary treatment stage in which some of the undissolved mass is allowed to settle out, leaving “primary” waste, the “primary” is then further treated in secondary and/or tertiary treatment stages, in which microorganisms are utilized to metabolize pollutants contained therein, resulting in conversion of complex organic matter into simpler organic compounds.
The treatment of the “primary” with microorganisms is often performed using one or both of two techniques: attached growth and suspended growth. In the attached growth process, microorganisms grow as a thick coat on a porous, immobilized support media known as trickling media. The waste stream is allowed to flow over or through the support medium, which is often shaped as a bed or column, so that the microorganisms are exposed to the pollutants for metabolization. Rock media is commonly used in such a manner.
While rock media does provide a suitable surface for the growth of microorganisms, it is quite dense at around 100 lb/ft3, and thus, relatively expensive to transport. Other less dense support media, such as plastics, are less expensive to transport, more costly to manufacture, and present a nonpolar surface which is not ideal as a media for promoting population by or with a polar substance, such as microorganisms.
In the suspended growth process, the microorganisms move freely about as flocs in a tank in which an influent stream constantly streams in and an effluent stream constantly flows out. In order to provide satisfactory treatment of the waste inside the tank, it is maintained in constant turbulence. Although the flocs are relatively lightweight, during periods of low flow through the tank the microorganisms will tend either to settle out or to wash out with the flow through the tank. As a result, the pollutants will not be metabolized into the simpler organic compounds due to a diminished concentration of organisms.
As noted above, solid growth media are used in many other processes, such as for the production of organic compounds in a bioreactor. In contrast to wastewater treatment, relatively pure strains of specialized microorganisms are employed which have the ability to synthesize specific organic compounds. However, much as in the trickling media process for wastewater treatment, microorganisms used for organic compound synthesis are immobilized upon a solid support in a relatively dense population. Likewise, this process also involves the same issues regarding transportation cost versus density of the solid growth media and cost of manufacturing the media.
In the remediation of hazardous waste sites, specific microorganisms are used that have the ability to metabolize specific hazardous pollutants into simpler organic compounds. In many gas separation processes, contaminated gases are passed through a sludge containing microorganisms which metabolize and thus remediate the pollutants. This type of bioremediation process is disclosed, for example, in U.S. Pat. Nos. 4,544,381 and 4,894,162. Similar to the suspended growth process used in secondary and tertiary wastewater treatment, low flow conditions tend to settle out or to wash out the microorganisms.
Another common method in gas separation processes for bioremediation is to pass contaminated gases through a bed of substrates in a bioreactor which carries microorganisms that degrade the pollutants contained in the gases. The prior art substrates used in this method have mainly been decomposable organic matters, such as peat, wood chips and other composts. However, the use of decomposable organic matters as the substrates for supporting and carrying the bioremediating microorganisms may be disadvantageous in that the substrates decompose and settle with time. Additionally, the organic substrates are not dimensionally stable over time. Such settlement and dimensional instability change the flow pattern of the gases fed through the bioreactor, creating undesirable flow patterns, and often create channeling that directs the influent gases to bypass substantial sections of the bioreactor, diminishing the efficiency of the reactor. Moreover, the organic substrates do not have appropriate configurations to allow the gases to pass through without a substantial pressure drop, and the organic substrates tend to get clogged as the biomass density increases in the reactor. Therefore, bioreactors employing current organic support materials require an increasingly high inflow pressure feeding the contaminated gases in order to overcome pressure losses created by the microbes populating the media.
Several solid carriers and polymeric composite products have been proposed for a variety of reasons. For example, Japanese Patent Publication JP 6-190385 discloses a bacterial carrier made by foaming an inorganically filled polyethylene or polypropylene. U.S. Pat. No. 5,503,738 discloses a macroporous substances coated with an adsorbent. U.S. Pat. No. 5,590,499 discloses an insulating wall element, wherein a mixture of sand and polyurethane fills in between regularly spaced brick fillets. Japanese Patent Publication Nos. JP 55-44866 and JP 6-296500, as well as German Patent Publication No. DE 37 04 802 A1, disclose other carriers and/or polymeric composite products. United States Published Patent Application Nos. US 2001/0002313 A1 (bioreactor media pellets) and US 2002/0015986 A1 (method for reducing the bioavailability of lead) disclose still other carriers and/or polymeric composite products. U.S. Pat. Nos. 3,232,865 (method for purifying wastewater), 3,646,715 (prefabricated building panel), 4,005,035 (high density rigid polyurethane foam products), 4,236,569 (foundry mold), 4,781,781 (solid polymeric material), 4,983,299 (removal of phenols from wastewater by a fixed bed reactor), 5,000,853 (biological treatment of sewage), 5,217,616 (removal of organic pollutants from water), 5,503,738 (biological remediation of vaporous pollutants), 5,863,789 (microorganism carrier for soil remediation), 5,962,309 (microorganism carrier for a fluidized bed) and U.S. Pat. No. 6,293,045 B1 (biodegradable mulch mat) disclose still other carriers and/or polymeric composite products.
None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed. Thus a light weight medium for growing microorganisms solving the aforementioned problems is desired.